Saudi-led warplanes bombed targets in Yemen's northerly Saada province, a stronghold of Iranian-allied Houthi forces, local officials said Wednesday, and a U.N. official accused both sides in the conflict of failing to respect international law.

Jets from a Saudi-led coalition also attacked Houthi-held locations in the south including the town of Dhalea and al-Anad air base, Yemen's largest, which lies in a strategic position commanding the approaches to the major southern port of Aden.

The Arab coalition, allied with southern secessionist forces, retook much of Aden last week in the first ground victory of their offensive to end Houthi control over much of Yemen and restore exiled President Abd-Rabbu Mansour Hadi.

There was no immediate word on casualties from the latest bombing raids.

Periodic shelling

Coalition forces have said Houthi forces based in Saada, near the Saudi-Yemeni border, have periodically shelled targets in southern Saudi Arabia during the conflict.

In the central city of Taiz, 10 Houthi fighters and five soldiers from forces loyal to Hadi's Saudi-based government were killed in clashes, residents and a local official said.

In New York, United Nations aid chief Stephen O'Brien said none of the warring parties in Yemen had observed a humanitarian pause in fighting intended to allow in emergency aid amid severe shortages of fuel, food and medicine.

A cease-fire called by the coalition to start on Sunday evening crumbled almost immediately, posing problems for relief organizations seeking to expand aid deliveries.

"Parties to the conflict continue to fail to meet their responsibilities under international humanitarian and international human rights laws," O'Brien told the 15-member U.N. Security Council. "We continue to witness the death and injury of civilians."

Near-total blockade

Yemen relies on imports, but a near-total blockade led by Saudi Arabia has slowed shipments to the Arabian Peninsula country to a trickle.

The Arab coalition is inspecting shipments in an effort to thwart any arms deliveries to the Houthis.

The World Health Organization said this week that according to data from health facilities in Yemen, 3,984 people had been killed and 19,347 had been injured between March 19 and July 19.

The Houthi movement was formed over a decade ago in Yemen's north to fight for the interests of Zaydi Shi'ites, a minority sect that ruled a 1,000-year kingdom in Yemen until 1962.

It rose to prominence last year when it seized the capital Sana’a and pushed Hadi aside in what it called a drive for clean government and a fair say for their followers in national affairs.